An installation switching apparatus is, for example, a circuit breaker. Such an installation switching apparatus is in particular a circuit breaker of the type which has an arc control device in which a switching arc that is created in the case of an isolation of the contact point under load or overload, or in the case of a short circuit, enters and therein is quenched. The arc gases herein are directed through the arc control device to the end of the latter at the exhaust air side, and therein are supplied to the upstream portion of an exhaust air duct within the circuit breaker.
Circuit breakers are usually used for interrupting an electrical current path that is routed between a source of electrical energy and an electrical load, so as to react to a defect that has arisen. Circuit breakers are often disposed beside one another in an installation distributor and attached to one or a plurality of bus bars. The contact point of a circuit breaker usually comprises at least one stationary contact piece and one movable contact piece. The circuit breaker opens the contact point in the case of a defect, for example in the case of a short circuit. A switching arc is created between the diverging contact pieces. Said arc is routed by way of arc guide rails to an arc control device. The latter is in most instances formed as a stack of sheet-metal quenching plates having a number of ferromagnetic plates that are stacked on top of one another at a parallel spacing, wherein the arc enters the stack of sheet-metal quenching plates at an entry side, is split into a line of part-arcs that in electrical terms are switched in series, such that the arc impedance is multiplied, the arc being quenched still within the pack of sheet-metal quenching plates. The arc gases accompanying the arc are ionized and thus electrically conductive. The positive pressure prevailing on the arc urges the arc gases through the arc control device, said gases exiting the sheet-metal quenching pack at the exhaust air side of the latter. Said arc gases, due to the electrical conductivity thereof, should exit the interior of the apparatus but not in the region of the bus bars, so as to prevent short circuits between the bus bars. It has therefore been proposed to configure an exhaust air duct in the interior of the apparatus, which in an upstream portion of said exhaust air duct receives the arc gases and in the downstream portion of said exhaust air duct releases said arc gases to the environment of the housing by way of an exhaust air opening in the housing wall. The exhaust air opening is attached to such a location of the housing that outflowing arc gases cannot make their way into the region of the bus bars.
Furthermore, a circuit breaker usually has a thermal over-current release which is formed by way of a strip of a thermostatic bimetal which bends in the case of an enduring over-current and, on account thereof, likewise causes an opening of the contact point. A set screw is usually provided for the thermal adjustment of the bimetal strip. Said set screw is in most instances formed as a cylinder screw. Such a solution is illustrated in WO 95/20237, for example. In order for the set screw to be adjusted, said set screw has to be accessible to an activation tool, for example a screw driver, from the outside of the housing. The position of the screw, once adjusted, should not be changed any more. Therefore, the opening leading to the set screw is usually closed once adjusted. Therefore a further opening in the housing of the circuit breaker is to be provided as the access opening to the set screw, and the closing of the opening upon adjustment is performed in an additional assembly step by adhesively bonding the opening or by adhesively bonding a cover part thereto. This is complex.